Monday, April 6, 2009

100W DC Motor Achieves Near 100% Efficiency

Researchers at Tokai University developed a brushless DC motor that coverts electric power to motor output at a conversion efficiency of more than 96%.

The announcement was made at the 56th Spring Meeting of the Japan Society of Applied Physics, which took place from March 30 to April 2, 2009, at the University of Tsukuba in Ibaraki Prefecture, Japan.

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The DC motor features a "rated output of about 100W" and uses iron-basedamorphous metal for the motor core (See related article). The conversion efficiency is as high as 96.5% when the output is around 100W.

This time, the high efficiency motor was realized by tracking down thecauses of energy loss and making some improvements to reduce the loss. Specifically, motor energy loss is attributable to (1) power consumption of the control circuit (controller loss), (2) loss from the coil winding (copper loss), (3) loss due to current surge in the core (iron loss) and (4) loss from rotation axis friction and air resistance (mechanical loss, windage loss).

The high efficiency of more than 96% was achieved mainly by improving (1) and (2). Specifically, a microcomputer featuring a low power consumption of 156mW was employed to reduce the controller loss. In addition, an inverter composed of nMOSFETs alone was used. This is because the on-state resistance of nMOSFET is lower than that of pMOSFET, Kimura said.

In respect to the copper loss, it was reduced by optimizing the thickness of the coil winding and the winding number. Copper loss generally increases as the current supplied to the motor becomes larger. Therefore, the reduction significantly contributes to the improvement, he said. The iron loss was reduced by using iron-based amorphous metal as the core material. This is because amorphous metal has low electron mobility, resulting in less current surge, Kimura said. However, the same material was used in the motor developed in 2003.